CEDAR RAPIDS — In the battle of out-of-state interest groups, NextGen Climate, which is backing Democrat Bruce Braley’s U.S. Senate bid, is claiming success in putting Republican Joni Ernst on the defensive.

After spending more than $3.7 million in Iowa to tie Ernst to the Koch brothers and Big Oil, opening nine offices and building a pool of 450 staff and volunteers, NextGen Climate says it is making climate change a wedge issue candidates can’t avoid.

KCRG-TV9 and The Gazette fact checked two of NextGen Climate’s ads. We determined one’s claim that Ernst would eliminate support for Iowa renewables was false, and one claiming a tax pledge signed by Ernst would benefit companies that sent jobs overseas as mostly true.

“In all the states, climate is a top tier issue,” NextGen Climate chief strategist Chris Lehane said in a conference call Wednesday. In some states, climate has become “a dominant or certainly a predominant issue over the last 30 days that corresponds with our efforts.”

“Want everyone running for office to have no choice but to have to talk about this because it is so salient to voters” whether it’s because of extreme weather, impacting their jobs in the renewable fuel industry, driving up insurance rates or affecting their health, he said.

Although Ernst has closed a 6 percentage point gap since May and is now tied with Braley, Lehane insisted the strategy is working.

Republicans, speaking on background, were dubious. They pointed to recent polls showing that jobs and the economy are still the top issues in voters’ minds and climate is, in many cases, polling in single digits.

Lehane, however, said NextGen Climate’s target is a “narrow band” of voters who are persuadable on the issue. Although not large in numbers, their impact may be outsized in what has become a dead even race for the Senate seat held by retiring Democrat Sen. Tom Harkin.

Republicans close to the Ernst campaign also noted she raised more money than Braley in the last quarter.

They were skeptical that Iowa voters will be swayed by the argument Ernst is bankrolled by the Koch brothers when Braley has benefited from the millions spent by NextGen Climate and its funder, Tom Steyer.

NextGen Climate is “giddy” to have Braley in its pocket, Republican Party of Iowa spokesman Jahan Wilcox said.

“Iowans should beware that NextGen is bankrolled by billionaire Tom Steyer, who stands against Iowa’s ethanol industry,” he added, referring to anti-ethanol statements by Steyer, a former hedge fund manager accumulated part of his fortune by investing in fossil fuel projects.

“I saw in the paper the other day that Al Gore was saying that maybe he shouldn’t have been for ethanol,” Steyer told Fortune magazine four years ago. “It’s kind of like duh! Did you ever take out your calculator on that one?”

Regardless, Lehane said the NextGen Climate campaign is having an impact. By questioning her support for renewable fuels, he said, the super PAC has forced her to defend her philosophical opposition to the Renewable Fuel Standard.

The Ernst declined to comment on NextGen Climate’s claims, but the candidates has pointed to her 100 percent voting record on renewable fuels in the Iowa Senate, where she was a sponsor of a resolution calling on the Environmental Protection Agency to maintain the RFS.

“I have a proven record,” Ernst said. “My opponents may try to confuse Iowans with spin, but facts are facts … I stand in strong support of the RFS.”

NextGen Climate plans to keep the pressure on Ernst through Election Day. Wednesday it expanded its get-out-the-vote efforts to focus attention on climate change and elect Braley.

It’s setting its sights on young voters, according to Iowa State Director Derek Eadon. NextGen Climate has determined 62 percent of voters age 18 to 34 believe climate change is a problem and want candidates to talk about it.

NextGen Climate will be a “massive presence” on campuses, Eadon said, and hopes to establish NextGen Climate Student Organizations at the three state universities.